1. Field of the Invention
This invention relates to a method of measuring and controlling the concentration of ozone by ultraviolet ray absorptiometry in an ozone weatherometer, which method can artificially promote and test those cracks of rubber products typified by car tires which are generated by ozone in air.
2. Description of the Prior Art
A conventional method of measuring and controlling the concentration of ozone by ultraviolet ray absorptiometry employs an arrangement such as that shown in FIG. 4 of the accompanying drawings, wherein dust of ozonized air 40 entering an ultraviolet ray absorption cell 44 from an ozone testing tank 1 is first removed by a filter 41. Then the ozonized air may enter an ultraviolet ray absorption cell 44 through either a bypass 42 or through a zero-gas filter 43, respectively, depending upon the state of a switching operation.
This switching operation is carried out continuously by automatic change-over valve 45 which effectively switches the path to the cell 44. Ultraviolet rays from a mercury lamp 46 are irradiated through the ultraviolet ray absorption cell 44 and are received by a measuring photo-receiver 47.
Assuming that a photocurrent flowing through the measuring photo-receiver 47 is Io when a gas made ozone-free after passing through the zero-gas filter 43 flows through the ultraviolet ray absorption cell 44, then the difference .DELTA.I=Io-Im has a proportional relation when the ozone concentration is in the pphm order. Therefore, the ozone concentration is calculated by an electrical calculation circuit which calculates this difference .DELTA.I. And, the concentration is displayed and recorded or merely displayed.
Incidentally,, reference numeral 48 in the drawing represents a suction port, 49 a quartz plate, 50 an exhaust port, 52 an exhaust processor, 53 a flow meter, 54 a flow regulating valve, 55 a pump and 56 exhaust.
The problem with the prior art technique described above is as follows. Since the ultraviolet rays (253.7 nm) for measuring ozone are absorbed by a large number of gases of organic solvents, e.g. benzene, acetone, toluene, etc. steam, SO.sub.2, and the like, it is an essential condition for the zero-gas filter to absorb and decompose only ozone but not to react at all with other gases in order to facilitate an accurate measurement of ozone concentration.
However, the zero-gas filter unavoidably adsorbs and decomposes the disturbing gases to some extents. In other words, the zero-gas filter decomposes and adsorbs 100% of ozone but at the same time decomposes and adsorbs about 20 to 30% of the disturbing gases, and its reaction with the disturbing gases is not completely zero. Particularly when the number of testpieces placed into the ozone testing tank is large, the disturbing gases such as the gases of the organic solvents occurring from the testpieces are not negligible and if there is any difference between when the disturbing gases pass through the bypass and when they pass through the zero-gas filter, this difference results in an error in the ozone concentration measured.
Ozone concentration measurement by ultraviolet ray absorptiometry has the advantages in that chemicals such as reagents that are required for a chemical analytical method are not all necessary and the measuring procedure is simple, but is not free from the drawback of the measurement error occurring due to the disturbing gases.
In accordance with the prior art method described above the measurement is carried out on the premise that any influence of the disturbing gases can be neglected, but the occurrence of the disturbing gases cannot be neglected on the number of testpieces, the difference of their material, the testing temperature, and so forth.
If the site of installation of the tester is the production site of rubber products, various organic matters are emitted during the production process carried out at the site and the air itself sucked into the testing tank contains large quantities of disturbing gases.
Therefore, when the ozone concentration of the testing tank is about 50 pphm, the disturbing gases sometime account for about 20 to 30% and in the case of automatic control, the ozone concentration inclusive of the disturbing gases is controlled as the ozone concentration, though the ozone value is substantially 80 to 70%. In the case of using an ozone concentration of 50 pphm, 40 to 35 pphm is the real ozone concentration and 20 to 15 pphm is sometimes a false ozone concentration due to the disturbing gases.
Even though the ozone concentration is apparently adjusted to 50 pphm, its value fluctuates so that the test results become different and judgement becomes difficult from time to time.
Accordingly, it has become necessary to eliminate in advance the disturbing gases such as the organic solvent gases which may be measured erroneously as ozone contained in air, to identify accurately the disturbing gases generated from the testpiece and to measure and control the concentration of ozone based on a value from which an influence of the disturbing gas component is eliminated.